Samples of porous high density polyethylene, aluminum oxide and cobalt-chromiummolybdenum ("Vitallium") alloy, each having interconnection pore sizes of 75, 150 and 250 micrometers will be implanted in the femora of adult mongrel canines. After a period of six months, allowing complete growth of bone into the pores of the samples, they will be removed and subjected to fracture toughness testing. The test used will be that of work-to-fracture. The test data will allow these porous materials to be compared on the basis of a mechanical design parameter (i.e. fracture toughness) measured under actual service conditions (i.e. when the pores are completely filled with bone). The results will be compared with the fracture toughness of native bone; inimplanted samples; and bulk (non porous) sample materials.